Zoom lens and camera

ABSTRACT

To obtain a high imaging performance even for a relatively long focal length in a zoom lens provided with an optical-path bending member for bending an optical path. The following are included: a first group of lenses G 1  having a positive refracting power, a second group of lenses G 2  having a negative refracting power, a third group of lenses G 3  having a positive refracting power, and a fourth group of lenses G 4  having a positive refracting power arranged in that order from the object side to the image surface side. Zooming is performed by moving the second group of lenses G 2  and fourth group of lenses G 4  along an optical axis. The first group of lenses G 1  is constituted of a group of positive lenses L 1  having a positive refracting power and an optical-path bending member L 2  for bending an optical path arranged in that order from the object side to the image face side.

FIELD OF THE INVENTION

The present invention relates to a zoom lens and a camera provided with the zoom lens.

BACKGROUND OF THE INVENTION

In recent years, there has been a demand for reducing size and thickness of a digital camera. There has also been a demand for reducing size, thickness, and cost of an image pickup optical system mounted on a digital camera. To meet these demands, an image-pickup optical system which has a reduced number of optical elements and is provided with an optical element for bending an optical path, such as a prism, has been put into practical use.

In addition, there has been a demand for a telephoto zoom lens which accommodates high pixel counts of a solid-state image pickup device such as a CCD by finely correcting an aberration, as well as providing for a long focal length while being sufficiently bright, providing f-number in the order of 5.0 or less, in order to increase the added value of a product.

For example, Japanese Patent Laid-Open Publication No. Sho 57-138612 discloses a telephoto zoom lens constituted of a first group of lenses having a positive refracting power, second group of lenses having a negative refracting power, third group of lenses having a positive refracting power, and fourth group of lenses having a positive refracting power, from the object side in that order.

However, the telephoto zoom lens disclosed in Japanese Patent Laid-Open Publication No. Sho 57-138612 has a linear optical axis and is not suitable for an image pickup device such as a thin digital camera demanded nowadays.

However, Japanese Patent Laid-Open Publication No. 2003-202500, Japanese Patent Laid-Open Publication No. Hei 8-248318, Japanese Patent Laid-Open Publication No.2000-131610, and Japanese Patent Laid-Open Publication No. 2005-173191 disclose an image pickup lens system constituted so that a high imaging performance can be obtained while it is compact and thin by providing an optical-path bending member such as a prism for bending the optical path for a first group of lenses.

FIG. 4 of Japanese Patent Laid-Open Publication No. 2003-202500 discloses an image pickup lens system in which a concave meniscus lens whose convex face is oriented toward the object side and a Plano convex lens whose convex face is oriented toward the object side are arranged from the object side in that order to the object side of a right-angle prism. Furthermore, FIG. 5 of Japanese Patent Laid-Open Publication No.2003-202500 discloses an image pickup lens system in which a biconcave lens, biconvex lens, and Plano convex lens whose convex face is oriented toward the object side are arranged in that order from the object side to the object side of a right-angle prism.

That is, Japanese Patent Laid-Open Publication No. 2003-202500 discloses an image pickup lens system in which a lens system having a positive refracting power is disposed to the object side of a right-angle prism. However, in the case of the image pickup lens system in which a lens system having a positive refracting power is disposed at the object side of the right-angle prism shown in FIGS. 4 and 5 of Japanese Patent Laid-Open Publication No. 2003-202500 because lenses disposed to the object side of the right-angle prism are separated from each other, the optical axis at the object side of the reflection face of the right-angle prism becomes long. Therefore, this may be an obstacle in reducing size and thickness of a camera.

Moreover, Japanese Patent Laid-Open Publication No. Hei 8-248318 and Japanese Patent Laid-Open Publication No. 2000-131610 disclose an image pickup lens system in which a lens having a negative refracting power is disposed to the object side of a prism for bending an optical path as a lens constituting a first group of lenses. Furthermore, Patent Document 5 discloses an image pickup lens system in which a first group of lenses is constituted of a prism having a negative refracting power and a lens having a positive refracting power from the object side in that order.

The f-number is represented by “f/D”, where f is the focal length of a lens and D is the entrance pupil diameter (effective diameter) of the lens. Therefore, in order to secure a certain degree of f-number at the telephoto side having a long focal length, it is necessary to secure a certain degree of large value for the entrance pupil diameter D.

Therefore, when a telephoto zoom lens having a long focal length while maintaining image brightness is arranged so that the object side of the reflection face of a prism has a negative refracting power, as shown in Japanese Patent Laid-Open Publication No. Hei 8-248318, Japanese Patent Laid-Open Publication No. 2000-131610, and Japanese Patent Laid-Open Publication No. 2005-173191, an incoming light flux diverges relative to an entrance pupil diameter. Therefore, it is necessary to use a relatively large prism or a group of lenses disposed at the image face side of the prism, which may be an obstacle in reducing size and thickness of a camera.

SUMMARY OF THE INVENTION

It is an advantage of the present invention to obtain a high imaging performance even with a relatively long focal length in a zoom lens provided with an optical-path bending member for bending an optical path.

A zoom lens of the present invention includes a first group of lenses having a positive refracting power, a second group of lenses having a negative refracting power, a third group of lenses having a positive refracting power, and a fourth group of lenses having a positive refracting power arranged in that order from the object side to the image side, and is constituted so as to perform zooming by moving the second group of lenses and the fourth group of lenses along the optical axis. The first group of lenses is constituted of a group of positive lenses having a positive refracting power and an optical-path bending member for bending an optical path from the object side in that order to the image side.

The group of positive lenses is constituted of a single lens having a positive refracting power for example. Moreover, it is permissible for the group of positive lenses to be constituted of a cemented lens obtained by cementing a single lens having a negative refracting power with a single lens having a positive refracting power from the object side to the image face side in that order. Furthermore, it is permissible for the group of positive lenses to be constituted of a cemented lens obtained by cementing a single lens having a negative refracting power and a single lens having a positive refracting power and a single lens having a positive refracting power arranged in that order from the object side to the image side.

In this case, the optical-path bending member is disposed towards the most image face side in the first group of lenses.

Moreover, it is preferable to satisfy a relation of 1.0<fl/fw<3.5 where fl is the focal length of all lens systems constituting the first group of lenses disposed to the object side of the optical-path bending member and fw is the focal length of all lens systems constituting the zoom lens at wide angle end.

Additionally, it is preferable for a zoom lens of the present invention to move the fourth group of lenses toward the third group of lenses along an optical path when focusing from an infinite object to a near range object, and to satisfy a relationship of 0.55<β4_(T)<0.92, 0.8<|β4_(T)/β4|<2.0, and 0.04<|D34_(W)/f4|<0.4, where β4_(W) is the lateral magnification of the fourth group of lenses when focusing on an infinite distance object at a wide angle end, β4_(T) is the lateral magnification of the fourth group of lenses when focusing on an infinite distance object at a telephoto end, D34_(W) is the air gap between the third group of lenses and the fourth group of lenses at a wide angle end, and f4 is the synthetic focal length of the fourth group of lenses.

Furthermore, it is preferable for the optical-path bending member to be a prism using a glass material for satisfying a relationship of 1.6<nd<1.85 and νd<40, where the nd is refraction index of the optical-path bending member of d-line and νd is the Abbe number of the optical-path bending member of d-line.

Furthermore, it is preferable for a zoom lens of the present invention to satisfy a relationship of d/fw<0.194, where d is the maximum image height on an image face and fw is the focal length of all lens systems constituting the zoom lens at wide angle end.

According to the present invention, a first group of lenses is constituted of a group of positive lenses having a positive refracting power and an optical-path bending member for bending an optical path from the object side in that order to the image side. Therefore, it is possible to relatively shorten the optical axis at the object side of the optical-path bending member while also securing a relatively bright f-number in the telephoto-side long focal length.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing an optical-axis cross section of the zoom lens of first example;

FIGS. 2A to 2C are illustrations showing various aberration diagrams at the short focal length end of the first example;

FIGS. 3A to 3C are illustrations showing various aberration diagrams of the intermediate focal length of the first example;

FIGS. 4A to 4C are illustrations showing various aberration diagrams of the long focal length end of the first example;

FIG. 5 is an illustration showing the optical-axis cross section of the zoom lens of second example;

FIGS. 6A to 6C are illustrations showing various aberration diagrams of the short focal length end of the second example;

FIGS. 7A to 7C are illustrations showing various aberration diagrams of the intermediate focal length of the second example;

FIGS. 8A to 8C are illustrations showing various aberration diagrams of the long focal length end of the second example;

FIG. 9 is an illustration showing the optical-axis cross section of the zoom lens of third example;

FIGS. 10A to 10C are illustrations showing various aberration diagrams of the short focal length end of the third example;

FIGS. 11A to 11C are illustrations showing various aberration diagrams of the intermediate focal length of the third example;

FIGS. 12A to 12C are illustrations showing various aberration diagrams of the long focal length end of the third example;

FIG. 13 is an illustration showing the optical-axis cross section of the zoom lens of fourth example;

FIGS. 14A to 14C are illustrations showing various aberration diagrams of the short focal length end of the fourth example;

FIGS. 15A to 15C are illustrations showing various aberration diagrams of the intermediate focal length of the fourth example;

FIGS. 16A to 16C are illustrations showing various aberration

diagrams of the long focal length end of the fourth example;

FIG. 17 is an illustration showing a state of the zooming operation of a zoom lens; and

FIG. 18 is an illustration showing a configuration of a digital camera on which a zoom lens is mounted.

DETAILED DESCRIPTION OF THE INVENTION

The best modes (hereafter referred to as embodiments) for executing the present invention are described below by referring to the accompanying drawings. FIGS. 1 to 4 are illustrations for a first example, FIGS. 5 to 8 are illustrations for a second example, FIGS. 9 to 12 are illustrations for a third example, and FIGS. 13 to 16 are illustrations for a fourth example.

First, matter common to each of the examples will be described.

In the following description, “Si” denotes an i-th face from the object side, “Ri” denotes the curvature radius of the face Si, “di” denotes a face interval on the optical axis between the i-th face and i+1-th face from the object side, “ndLi” denotes a refraction index of a d-line (wavelength of 587.6 nm) of a lens Li, “νdLi” denotes an Abbe number of d-line of the lens Li, “f” denotes a focal length of all lens systems, “Fno” denotes an open f-number, and “ω” denotes a half field angle.

Moreover, a lens constituted of an aspherical surface is included in the lenses used for the examples.

The aspherical lens is shown by the following expression, where “x” is the distance from the vertex of a lens face to an optical-axis direction, “y” is the distance from the vertex of the lens face to the direction vertical to the optical axis, R is paraxial curvature radius, and k, A, B, C, and D are aspherical coefficients. $x = {\frac{\left( {1/R} \right)y^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)\left( {y/R} \right)^{2}}}} + {A\quad y^{4}} + {B\quad y^{6}} + {C\quad y^{8}} + {D\quad y^{10}}}$

The zoom lenses of the first to fourth examples are respectively constituted of a first group of lenses G1 having a positive refracting power, a second group of lenses G2 having a negative refracting power, a third group of lenses G3 having a positive refracting power, and a fourth group of lenses G4 having a positive refracting power in that order from the object side to the image face IMG as shown in FIGS. 1, 5, 9, and 13. FIGS. 1, 5, 9, and 13 respectively show the positional relation between the lens groups at wide angle ends.

Moreover, an aperture IR is disposed between the second group of lenses G2 and the third group of lenses G3. Furthermore, an optical equivalent member IF is disposed between the fourth group of lenses G4 and the image face IMG. The optical equivalent member IF is constituted of a low-pass filter, infrared cut filter, and the cover glass of a solid-state image pickup device arranged in that order from the object side to the image face side for example.

The second group of lenses G2 is mainly involved with zooming and moves from the object side to the image side along the optical axis at the time of zooming from a wide angle end to a telephoto end. The fourth group of lenses G4 compensates the movement of a focal point according to the movement of the second group of lenses G2 by moving in a non-linear manner along the optical axis.

The first group of lenses G1 is constituted of a group of positive lenses having a positive refracting power and an optical-path bending member for bending an optical path by approx. 90°.

Conventionally, in the case of a zoom lens provided with an optical-path bending member for bending an optical path, a negative lens having a negative refracting power is disposed to the object side of the optical-path bending member. By using this configuration, it is possible to make light flux from a wide field angle enter a lens at the wide angle side. However, by disposing the negative lens to the object side of the optical-path bending member, it is necessary to increase the optical-path bending member and a group of lenses disposed to the image side of the optical-path bending member in size because an incoming light flux diverges compared to the entrance pupil diameter D. Particularly, to secure a relatively bright f-number also at the telephoto side which becomes a long focal length, it is necessary to secure a certain degree of size for the entrance pupil diameter D. Therefore, in the case of a configuration in which the negative lens is disposed to the object side of the optical-path bending member, it is necessary to increase the size of the optical-path bending member and a group of lenses disposed to the image face side of the optical-path bending member.

Therefore, in the case of this example, a group of positive lenses is disposed to the object side of an optical-path bending member. Thereby, a relatively bright f-number is also secured in a long focal length at the telephoto side and it is possible to shorten the optical axis at the object side of the optical-path bending member.

Moreover, in the case of this example, an optical-path bending member is disposed to the most image face side of the first group of lenses G1. That is, a lens for constituting the first group of lenses G1 is not disposed to the image face side of the optical-path bending member. As a result, it is possible to shorten the optical axis at the image face side of the optical-path bending member while securing the moving range of the second group of lenses moving along the optical axis when performing zooming.

Furthermore, in the case of this example, zooming is performed when the second group of lenses G2 moves linearly as shown in movement locuses M2 and M4 in FIGS. 1, 5, 9, and 13. Furthermore, to correct the movement of a focus position due to the movement of the second group of lenses G2, the fourth group of lenses G4 moves nonlinearly. Particularly, as shown by movement locuses M4 and M4′ in FIG. 17, when the fourth group of lenses is moved to the object side to focus, it is preferable to move the second group of lenses G2 and fourth group of lenses G4 so as to satisfy the following expressions (1) to (3). 0.55<β4_(T)<0.92 . . .   (1) 0.8<|β4_(T)/β4_(W)|<2.0 . . .   (2) 0.04<|D34_(W) /f4|<0.4 . . .   (3)

In this case, it is assumed that the lateral magnification of the fourth group of lenses G4 is β4_(W) when focusing on an infinite object at a wide angle end, the lateral magnification of the fourth group of lenses G4 when focusing an infinite object at a telephoto end is β4_(T), the air gap between the third group of lenses G3 and the fourth group of lenses G4 at a wide angle end is D34_(W), and the synthetic focal length of the fourth group of lenses G4 is f4.

Expression (1) shows the condition of the air gap between the fourth group of lenses G4 and the image surface IMG at a telephoto end focal length. When the lateral magnification β4_(T) of the fourth group of lenses G4 exceeds the upper limit of the expression (2), it is difficult to secure a space in which the optical equivalent member IF is disposed between the fourth group of lenses G4 and the image face IMG. However, when the lateral magnification β4_(T) of the fourth group of lenses G4 does not reach the lower limit of the expression (2), a space for the fourth group of lenses G4 to move to the third group of lenses-G3 side is restricted when adjusting focus. Therefore, the lower limit of a distance up to an object which can be focused by moving the fourth group of lenses G4 along the optical axis is restricted at the time of close range photographing. That is, the shortest object distance at which imaging is preferably performed is increased.

Moreover, the expression (2) shows a condition for the difference between the air gap between the fourth group of lenses G4 and the image face IMG when performing zooming at a wide angle end and the air distance between the fourth group of lenses G4 and the image face IMG when performing zooming at a telephoto end. When the difference exceeds the upper limit of the expression (2), the moving range of the fourth group of lenses G4 when performing zooming increases, the length of a group of lenses constituting a zoom lens in the optical axis direction increases, and these become obstacles for decrease in size and thickness. It is more preferable that the expression (2) satisfies a relation of 0.8<|β4_(T)/β4_(W)|<1.4.

Moreover, the expression (3) shows a condition of the air gap between the third group of lenses G3 and the fourth group of lenses G4 at a wide-angle-end focal length. When |D34_(W)/f4| does not reach the lower limit of the expression (3), a space for the fourth group of lenses G4 to move to the third group of lenses-G3 side is restricted when adjusting a focus. Therefore, the lower limit of a distance up to an object which can be focused by moving the fourth group of lenses G4 along the optical axis is restricted at the time of close-range photographing.

As described above, it is possible to shorten the entire length of the optical axis while securing the movement space of the fourth group of lenses G4 necessary for focus adjustment in connection with focus movement due to zooming by moving the second group of lenses G2 and fourth group of lenses G4 so as to satisfy the expressions (1) to (3).

Moreover, it is preferable that |fl/fw| satisfies the following expression (4), where fl is the focal length of an optical member (that is, the above-described group of positive lenses) constituting the first group of lenses G1 disposed to the object side of the optical-path bending member and fw is the focal length of all lens systems constituting a zoom lens at a wide angle end: 1.0<f1/fw<3.5 . . .   (4)

When |fl/fw| does not reach the lower limit of the expression (4), the positive refracting power of an optical member disposed to the object side of the optical-path bending member becomes too strong. Therefore, it is difficult to secure a relatively long focal length and constitute a telephoto zoom lens by disposing this lens. Moreover, it is difficult to secure an optical-path length sufficient to bend the optical path of the light ray refracted and transmitted in this optical member by approx. 90° by the optical-path bending member.

Furthermore, when |fl/fw| exceeds the upper limit of the expression (4), the positive refracting power of the optical member disposed to the object side of the optical-path bending member becomes too weak. Therefore, it is necessary to increase effective diameters of the optical-path bending member, second group of lenses G2, and third group of lenses G3 to be disposed to the image side of the optical member and lengthen the entire optical axis. Therefore, this case becomes an obstacle for decrease of a camera in size and thickness. It is more preferable that the expression (4) satisfies a relationship of 1.8<fl/fw<3.5.

Moreover, when using a glass prism for the optical-path bending member and assuming the refraction index of d-line of the glass prism as nd and the Abbe number of the d-line as νd, it is preferable that the following expressions (5) and (6) are satisfied. 1.6<nd<1.85 . . .   (5) νd<40 . . .   (6)

A glass material in which the refraction index nd exceeds 1.85 which is the upper limit of the expression (5) and the Abbe number νd exceeds 40 which is the upper limit of the expression (6) is generally expensive, and it becomes an obstacle for reduction of the manufacturing cost.

EXAMPLE 1

Matter specific to the zoom lenses of the first to fourth examples will be respectively described below. The zoom lenses of the first to fourth examples can be mounted on various cameras such as a digital camera, monitoring camera, and in-vehicle camera.

Moreover, in the case of each of the following examples, an optical system which can be changed in a range in which the maximum half field angle ω mainly effective for infinite focusing is approx. 11° or less is described.

In general, it is known that the following relationship is effected between ω, d, and f, where d is the effective image circle diameter of an image (maximum image height on image) and f is a focal length. d=f×tanω   

That is, in the case of each of the following examples, a zoom lens system in which “d/fw” satisfies the following expression, where fw is the focal length of all lens systems constituting a zoom lens at a wide angle end, is described. d/fw<tan (11°)=0.194 . . .   (7)

FIRST EXAMPLE

In the case of the zoom lens of the first example, a group of positive lenses constituting the first group of lenses G1 is constituted of a single lens L1 having a positive refracting power as shown in FIG. 1. The second group of lenses G2 is constituted of a biconcave lens L3 and a cemented lens obtained by cementing a biconcave lens L4 and biconvex lens L5 from the object side in that order. The third group of lenses G3 is constituted of a biconvex lens L6 and a cemented lens obtained by cementing a biconvex lens L7 and biconcave lens L8 from the object side in that order. In addition, the fourth group of lenses G4 is constituted of a cemented lens obtained by cementing a biconvex lens L9 and biconcave lens L10.

In this case, it is preferable that the single lens L1 uses a glass material having an Abbe number of 62 or more. As a result, it is possible to preferably correct axial chromatic aberration which generally becomes a problem at the telephoto side.

Table 1 shows numerical data values of the zoom lens of the first example. In Table 1, three values shown after “f”, “Fno”, and “ω” show a focal length, f-number, and half field angle respectively in a short focal length end (wide angle end), intermediate focal length, and long focal length end (telephoto end). TABLE 1 f = 20.0-28.28-40.01 Fno = 4.71-4.71-4.63 ω = 10.5°-7.3°-5.1° Lens Face Curvature Face interval Refraction Abbe number number number radius R d index ndL νdL L1 S1 R1 31.624 d1 1.800 ndL1 1.4970 νdL1 81.6 S2 R2 1380.000 d2 0.600 — — L2 S3 R3 INF d3 13.000 ndL2 1.8467 νdL2 23.8 S4 R4 INF d4 Variable — — L3 S5 R5 −12.672 d5 0.800 ndL3 1.8467 νdL3 23.8 S6 R6 53.978 d6 0.600 — — L4 S7 R7 −15.118 d7 0.700 ndL4 1.7495 νdL4 35.0 L5 S8 R8 10.353 d8 2.000 ndL5 1.8052 νdL5 25.5 S9 R9 −11.050 d9 Variable — — IR S10 R10 — d10 0.500 — — L6 S11 R11 10.737 d11 2.000 ndL6 1.5891 νdL6 61.2 S12 R12 −52.372 d12 0.500 — — L7 S13 R13 12.562 d13 2.800 ndL7 1.5891 νdL7 61.3 L8 S14 R14 −7.281 d14 0.550 ndL8 1.6477 νdL8 33.8 S15 R15 7.674 d15 Variable — — L9 S16 R16 23.274 d16 2.000 ndL9 1.5814 νdL9 40.9 L10 S17 R17 −5.950 d17 0.600 ndL10 1.5891 νdL10 61.3 S18 R18 41.160 d18 Variable — — IF S19 R19 INF d19 1.500 ndL11 1.5168 νdL11 64.2 S20 R20 INF d20 — — —

Moreover, the face S12 at the image face side of the biconvex lens L6 constituting the third group of lenses G3 is constituted of an aspherical surface. Table 2 shows aspherical coefficients on the face S12. TABLE 2 Face number k A B C D S12 −3.7600E−01 0.0000E+00 −8.4193E−07 7.4374E−08 0.0000E+00

“E” in Table 2 denotes an exponential notation using 10 as the base part (the same applies to Tables 6, 10, and 14 below.)

Moreover, Table 3 shows values at a short focal length end, intermediate focal length, and long focal length end of face intervals d4, d9, d15, and d18 variable due to zooming. TABLE 3 Focal length f 20.001 28.284 40.014 Face interval d4 1.000 10.371 19.403 Face interval d9 19.902 10.531 1.500 Face interval d15 5.037 4.956 9.681 Face interval d18 12.372 12.453 7.727

In addition, Table 4 shows values of parameters of conditional expressions (1) to (6) in the first example. TABLE 4 (1) fl/fw 3.25 (2) β4T 0.816 (3) | β4T/β4w| 1.057 (4) | D34w/f4| 0.05 (5) nd 1.8467 (6) νd 23.8

FIGS. 2 to 4 are aberration diagrams at a short focal length end, intermediate focal length, and long focal length end of the zoom lens of the first example. In FIGS. 2 to 4, <A> denotes spherical aberration, a continuous line denotes the d-line, a broken line denotes the F-line, and a long dashed short-dashed line denotes spherical aberration on the C-line. Moreover, <B> denotes astigmatism, a continuous line denotes a value on a sagittal image surface, and a broken line denotes a value on a tangential image surface. <C> denotes a distortion. The same applies to FIGS. 6 to 8 and FIGS. 10 to 12 below.

SECOND EXAMPLE

A second example will now be described. As shown in FIG. 5, the second example is different from the first example in that a group of positive lenses constituting the first group of lenses G1 is constituted of a cemented lens obtained by cementing a concave meniscus lens L1 whose convex face is oriented toward the object side and having a negative refracting power and a biconvex lens L2 having a positive refracting power from the object side in that order. Moreover, the second example is different from the first example in that the fourth group of lenses G4 is constituted of a convex meniscus lens L10 whose convex face is oriented toward the object side and having a positive refracting power.

Thus, by disposing the cemented lens having a positive refracting power to the object side of the optical-path bending member, it is possible to further correct axial chromatic aberration compared to when constituting the group of positive lenses by a single lens, and thus obtain a more-preferable focusing performance. Therefore, it is possible to provide a zoom lens corresponding to a longer focal length.

Table 5 shows numerical value data of the zoom lens of the second example. TABLE 5 f = 20.5-37.40-70.00 Fno = 4.86-4.89-4.96 ω = 10.2°-5.5°-2.9° Lens Face Curvature Face interval Refraction Abbe number number number radius d index ndL νdL L1 S1 R1 22.994 d1 0.750 ndL1 1.7495 νdL1 35.0 L2 S2 R2 13.308 d2 2.800 ndL2 1.5891 νdL2 61.3 S3 R3 −146.940 d3 0.300 — — L3 S4 R4 INF d4 13.000 ndL3 1.8467 νdL3 23.8 S5 R5 INF d5 Variable — — L4 S6 R6 −51.688 d6 0.800 ndL4 1.8161 νdL4 46.6 S7 R7 16.471 d7 0.600 — — L5 S8 R8 −19.433 d8 0.700 ndL5 1.8061 νdL5 40.7 L6 S9 R9 10.774 d9 1.800 ndL6 1.8467 νdL6 23.8 S10 R10 −49.283 d10 Variable — — IR S11 R11 — d11 0.500 — — L7 S12 R12 8.240 d12 2.300 ndL7 1.5891 νdL7 61.2 S13 R13 −36.158 d13 0.200 — — L8 S14 R14 11.143 d14 2.000 ndL8 1.5891 νdL8 61.3 L9 S15 R15 −31.377 d15 0.800 ndL9 1.6477 νdL9 33.8 S16 R16 5.614 d16 Variable — — L10 S17 R17 13.100 d17 1.500 ndL10 1.4970 νdL 10 81.6 S18 R18 26.470 d18 Variable — — IF S19 R19 INF d19 1.500 ndL11 1.5168 νdL 11 64.2 S20 R20 INF — —

FIG. 6 shows aspherical coefficients on the face S12 at the object side of the biconvex lens L7 constituting the third group of lenses G3. TABLE 6 Face number k A B C D S12 −9.8200E−01 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

Table 7 shows values at a short focal length end, intermediate focal length, and long focal length end of face intervals d5, d10, d16, and d18 variable by zooming. TABLE 7 Focal length f 20.502 37.399 70.003 Face interval d5 0.700 8.18 14.593 Face interval d10 15.393 7.913 1.500 Face interval d16 9.009 6.13 20.487 Face interval d18 12.491 15.37 1.013

Table 8 shows values of parameters of conditional expressions (1) to (6) in the second example. TABLE 8 (1) fl/fw 1.99 (2) β4T 0.9021 (3) | β4T/β4w| 1.337 (4) | D34w/f4| 0.18 (5) nd 1.8467 (6) νd 23.8

FIGS. 6 to 8 are aberration diagrams in the second example. As shown in FIGS. 6 to 8, meanings shown by <A> to <C> are the same as the case of FIGS. 2 to 4.

THIRD EXAMPLE

A third example will be described below. As shown in FIG. 9, the third example is different from the second example in that the third group of lenses G3 is constituted of the biconvex lens L7 having a positive refracting power and a concave meniscus lens L8 whose convex face is oriented toward the object side and having a negative refracting power, arranged in that order from the object side.

Table 9 shows numerical value data of the zoom lens of the third example. TABLE 9 f = 20.0-37.11-59.99 Fno = −4.76-4.99-4.92 ω = 10.5°-5.5°-3.4° Lens Face Curvature Face interval Refraction Abbe number number number radius R d index ndL νdL L1 S1 R1 24.638 d1 0.750 ndL1 1.7495 νdL1 35.0 L2 S2 R2 13.773 d2 2.800 ndL2 1.5891 νdL2 61.3 S3 R3 124.680 d3 0.400 — — L3 S4 R4 INF d4 13.000 ndL3 1.8467 νdL3 23.8 S5 R5 INF d5 Variable — — L4 S6 R6 −54.920 d6 0.800 ndL4 1.8161 νdL4 46.6 S7 R7 17.080 d7 0.600 — — L5 S8 R8 −22.764 d8 0.700 ndL5 1.8061 νdL5 40.7 L6 S9 R9 8.650 d9 1.800 ndL6 1.8467 νdL6 23.8 S10 R10 −198.370 d10 Variable — — IR S11 R11 — d11 0.500 — — L7 S12 R12 6.219 d12 3.000 ndL7 1.5891 νdL7 61.2 S13 R13 −23.520 d13 0.917 — — L8 S14 R14 11.742 d14 0.800 ndL8 1.5891 νdL8 61.3 S15 R15 4.934 d15 Variable — — L9 S16 R16 9.738 d16 1.500 ndL9 1.4875 νdL9 70.4 S17 R17 16.563 d17 Variable — — IF S18 R18 INF d18 1.500 ndL10 1.5168 νdL10 64.2 S19 R19 INF — — —

Table 10 shows aspherical coefficients at the face S12 of the biconvex lens L7 constituting the third group of lenses G3 at the object side and image side S13 of the biconvex lens L7. TABLE 10 Face number k A B C D S12 −1.4766E+00 3.3200E−04 −7.0583E−06 8.1340E−09 0.0000E+00 S13 1.61655E+00 1.7900E−04 −8.7983E−06 5.1447E−08 0.0000E+00

Table 11 shows values of face intervals d5, d10, d15, and d17 variable by zooming at the short focal length end, intermediate focal length, and long focal length end. TABLE 11 Focal length f 19.999 34.114 59.990 Face interval d5 0.700 8.125 13.604 Face interval d10 14.404 6.979 1.500 Face interval d15 11.323 5.359 6.500 Face interval d17 10.177 16.141 15.000

Table 12 shows values of parameters of conditional expressions (1) to (6) in the third example. TABLE 12 (1) fl/fw 2.13 (2) β4T 0.5526 (3) | β4T/β4w| 0.837 (4) | D34w/f4| 0.25 (5) nd 1.8467 (6) νd 23.8

FIGS. 10 to 12 are aberration diagrams in the third example. Meanings shown by <A> to <C> in FIGS. 10 to 12 are the same as the case of FIGS. 2 to 4.

FOURTH EXAMPLE

A fourth example will now be described. As shown in FIG. 13, the fourth example is different from the second example in that the first group of lenses G1 is constituted of a cemented lens obtained by cementing the concave meniscus lens L1 whose convex face is oriented toward the object side and having a negative refracting power and biconvex lens L2 having a positive refracting power, biconvex lens L3 having a positive refracting power, and optical-path bending member L4 from the object side in that order.

Thus, by constituting a group of positive lenses from the cemented lens obtained by cementing the concave meniscus lens L1 and biconvex lens L2 and biconvex lens L3, it is possible to simultaneously correct chromatic difference of magnification generated out of an axis, image face curvature, and axial chromatic aberration and obtain more preferable imaging performance.

Table 13 shows numerical value data of the zoom lens of the fourth example. TABLE 13 f = 20.0-34.7-60.01 Fno = 4.92-4.93-4.87 ω = 10.3°-5.9°-3.4° Lens Face Curvature Face interval Refraction Abbe number number number radius R d index ndL νdL L1 S1 R1 500.000 d1 0.900 ndL1 1.8061 νdL1 40.7 L2 S2 R2 22.301 d2 2.500 ndL2 1.5168 νdL2 64.2 S3 R3 −63.748 d3 0.200 — — L3 S4 R4 22.433 d4 2.000 ndL3 1.5891 νdL3 61.3 S5 R5 −180.211 d5 0.300 — — L4 S6 R6 INF d6 13.000 ndL4 1.8467 νdL4 23.8 S7 R7 INF d7 Variable — — L5 S8 R8 −35.254 d8 0.800 ndL5 1.8161 νdL5 46.6 S9 R9 19.465 d9 0.600 — — L6 S10 R10 −32.314 d10 0.700 ndL6 1.8061 νdL6 40.7 L7 S11 R11 7.124 d11 1.800 ndL7 1.8467 νdL7 23.8 S12 R12 77.809 d12 Variable — — IR S13 R13 — d13 0.500 — — L8 S14 R14 8.296 d14 1.800 ndL8 1.5891 νdL8 61.2 S15 R15 −22.074 d15 0.300 — — L9 S16 R16 10.811 d16 2.300 ndL9 1.5891 νdL9 61.3 L10 S17 R17 −15.633 d17 0.800 ndL10 1.6477 νdL10 33.8 S18 R18 5.600 d18 Variable — — L11 S19 R19 14.906 d19 1.500 ndL11 1.4875 νdL11 70.4 S20 R20 22.659 d20 Variable — — IF S21 R21 INF d21 1.500 ndL12 1.5168 νdL12 64.2 S22 R22 INF — — —

Table 14 shows an aspherical coefficient of the biconvex lens L8 constituting the third group of lenses G3 on the face S14 at the object side. TABLE 14 Face number k A B C D S14 −1.3119E+00 0.0000E+00 −3.0304E−06 1.3919E−07 0.0000E+00

Table 15 shows values of face intervals d7, d12, d18, and d20 variable by zooming at the short focal length end, intermediate focal length, and long focal length end. TABLE 15 Focal length f 20.007 34.651 60.012 Face interval d7 0.700 7.066 12.604 Face interval d12 13.404 7.038 1.500 Face interval d18 17.000 6.000 15.000 Face interval d20 2.500 13.500 4.500

Table 16 shows values of parameters of conditional expressions (1) to (6) in the fourth example. TABLE 16 (1) fl/fw 1.86 (2) P4T 0.8867 (3) | β4T/β4w| 0.974 (4) | D34w/f4| 0.202 (5) nd 1.8467 (6) νd 23.8

FIGS. 14 to 16 are aberration diagrams in the fourth example. Meanings shown by <A> to <C> in FIGS. 14 to 16 are the same as for FIGS. 2 to 4.

An image pickup device on which the zoom lens is mounted is described below. FIG. 18 is an illustration showing a configuration of a digital camera on which the above zoom lens is mounted. The digital camera is roughly divided into a lens block 10 for obtaining the image of an object and body portion 20 for performing various controls necessary for various processing of image-pickup signals and image pickup. The lens block 10 is provided with a zoom lens 12 constituted of the described four lens groups and a solid-state image pickup device 14 for converting an object image acquired by the zoom lens 12 into electrical signals. The solid-state image pickup device 14 outputs the object image converted into electrical signals to the body portion 20 as image data.

In the case of the body portion 20, a control portion 24 executes various processing in accordance with instructions from a user input through an operating portion 26. Moreover, a signal processing portion 28 applies various signal processing such as A/D conversion and noise removal to the image data outputted from the solid-state image pickup device 14. The signal-processed image data is output to a display portion 30 and a recording medium 32. The recording medium 32 is a data storage medium constituted of a memory card or the like and picked-up image data is recorded in the recording medium. The display portion 30 is a display unit such as an LCD and a user confirms a picked-up image through the display portion 30. A lens driving control portion 22 outputs a driving signal to a lens moving mechanism mounted on a zoom lens when focusing or zooming is necessary to instruct movement of lens groups. The motor of the lens moving mechanism mounted on the zoom lens moves a group of lenses in accordance with the instruction.

PARTS L1ST

-   10 lens block -   12 zoom lens -   14 image pick-up device -   20 body portion -   22 lens driving control portion -   24 control portion -   26 operating portion -   28 signal processing portion -   30 display portion -   32 recording medium -   d7 face intervals -   d12 face intervals -   d18 face intervals -   d20 face intervals -   G1 first group of lenses -   G2 second group of lenses -   G3 third group of lenses -   G4 fourth group of lenses -   IMG image face -   IF optical equivalent member -   IR lens number -   L1 single lens -   L1 concave meniscus lens -   L2 biconvex lens -   L3 biconcave lens -   L3 binconvex lens -   L4 biconcave lens -   L4 optical path bending member -   L5 biconvex lens -   L6 biconvex lens -   L7 biconvex lens -   L8 biconcave lens -   L8 concave meniscus lens -   L8 biconvex lens -   L9 biconvex lens -   L10 biconcave lens -   L10 convex meniscus lens -   M2 movement locuses -   M4 movement locuses -   M4′ movement locuses -   S12 face -   S13 image side -   S14 face -   <A> spherical aberration -   <B> astigmatism -   <C> distortion 

1. A zoom lens comprising: a first group of lenses having a positive refracting power; a second group of lenses having a negative refracting power; a third group of lenses having a positive refracting power; and a fourth group of lenses having a positive refracting power, the first through fourth groups of lenses being formed in that order from an object side toward an image surface side, wherein the zoom lens is configured such that zooming is performed by moving the second group of lenses and the fourth group of lenses along an optical axis, and the first group of lenses comprises: a group of positive lenses having a positive refracting power; and an optical path bending member that bends an optical path, the group of positive lenses and the optical path bending member being formed in that order from the object side toward the image surface side.
 2. The zoom lens according to claim 1, wherein the group of positive lenses comprises a single lens having a positive refracting power.
 3. The zoom lens according to claim 1, wherein the group of positive lenses comprises a cemented lens obtained by cementing a single lens having a negative refracting power with a single lens having a positive refracting power from the object side in that order to the image face side.
 4. The zoom lens according to claim 1, wherein the group of positive lenses comprises a cemented lens obtained by cementing a single lens having a negative refracting power with a single lens having a positive refracting power, and a single lens having a positive refracting power, arranged in that order from the object side to the image face side.
 5. The zoom lens according to any one of claims 1 to 4, wherein the optical-path bending member is disposed to the most image surface side among the first group of lenses.
 6. The zoom lens according to claim 1, wherein a relationship of 1.0<fl/fw<3.5 is satisfied where fl is the focal length of all lens systems constituting the first group of lenses disposed to the object side of the optical-path bending member and fw is the focal length of all lens systems constituting the zoom lens at the wide angle end.
 7. The zoom lens according to claim 1, wherein the fourth group of lenses is moved to the third group of lenses along the optical axis when focusing from an infinite object to a near range object, and the following relationships are satisfied: 0.55<β4_(T)<0.92, 0.8<|β4_(T)/β4_(W)|<2.0, and 0.04<|D34_(W) /f4|<0.4 where; β4_(W) is the lateral magnification of the fourth group of lenses when focusing on an infinite object at a wide angle end, β4_(T) is the lateral magnification of the fourth group of lenses when focusing on an infinite object at a telephoto end, D34_(W) is the air gap between the third group of lenses and the fourth group of lenses at a wide angle end, and f4 is the synthetic focal length of the fourth group of lenses.
 8. The zoom lens according to claim 1, wherein the optical-path bending member is a prism using a glass material for satisfying a relationship of 1.6<nd<1.85 and νd<40, where nd is the refractive index of the optical-path bending member at a d-line and νd is the Abbe number of the optical-path bending member on the d-line.
 9. The zoom lens according to claim 1, wherein a relation of d/fw<0.194 is satisfied where d is the maximum image height on an image face and fw is the focal length of all lens systems constituting the zoom lens at a wide angle end.
 10. A camera provided with the zoom lens described in claim 1 and a solid-state image pickup device disposed to the image face side of the zoom lens. 